The invention relates to an engine with counter-rotating rotors, which are coaxially arranged and are driven via a shaft by a turbine whose working medium is supplied by a gas generator with an air inlet.
In engines with counter-rotating rotors or propellers, the air inlet for the gas generator or the core engine is arranged either before or after the rotors. In known engines, in which the air inlet is arranged before (in the axial direction) the rotors, the rotors are arranged coaxially in the region of the low-pressure turbine, one rotor being connected to the rotating low-pressure turbine stator and the other to the low-pressure turbine rotor.
In other known engines, in which the core engine is arranged with its air inlet behind the rotors, the rotors are generally driven via a gear by a high-speed low-pressure turbine. The rotors are supported in the engine casing by a floating bearing arrangement, one of the rotors being supported on the other. A problematic feature is that in the case of engines with counter-rotating rotors, low noise figures can only be achieved when the axial distance between the rotors is relatively large. In the case of a large distance between the rotors, however, their floating bearing arrangement leads to mechanically unfavorable designs, which are difficult to deal with, because all the forces generated by the rotors must, furthermore, be conducted via the casing into the engine suspension. In addition, a construction based on rotors arranged at a large axial distance from one another and on an engine air inlet located behind them leads to a long and heavy construction, in which the position of the center of gravity of the engine is displaced in a manner unfavorable to its installation.
A gas turbine engine is known from U.S. Pat. No. 4,860,537 in which an air inlet is arranged between two counter-rotating fan rotors. The fan rotors are directly coupled to a turbine and are driven by two separate drive shafts. A disadvantageous feature of this arrangement is that two shafts have to be led through the core engine. Because of the low rotational speed of the fan rotors, this involves slowly rotating shafts, which have a large diameter in order to be able to transmit the high torques.
The fan engine revealed in U.S. Pat. No. 5,010,729 has a fan rotor with an air inlet arranged axially behind it for the core engine, the fan rotor being driven by two counter-rotating shafts via two gears whose internal gearwheels are fixed to the casing.
The invention is based on the object of improving an engine, of the generic type described at the beginning, in such a way that the noise annoyance due to the rotors is kept low in association with the smallest possible axial installation length.
This object is achieved, in accordance with the invention, by the characterizing features of claim 1.
This arrangement of the air inlet or the suction opening makes it possible to arrange the support bearing of the rotors in the vicinity of their centers of gravity even in the case of a large axial distance between the rotors. For further noise reduction, the axial distance between the rotors can, in addition, be increased without difficulty without disadvantages appearing with respect to the mechanical loads on the engine.
In a preferred embodiment, a (support) casing of the rotors is arranged in the drive shaft of the rear (in the axial direction) rotor.
Both bearings of the rear rotor and the floating bearing of the front rotor are preferably arranged in the (support) casing and the fixed bearing of the front rotor is preferably arranged as an intermediate shaft bearing on the shaft of the rear rotor.
It is advantageous for the rear rotor to be driven by a rotating cascade arranged in the air inlet opening, this cascade being preferably designed in such a way that the swirl generated in the airflow by the front rotor is essentially cancelled out. This achieves the effect that the flow into the casing is swirl-free.
Maximum preference is given to the single internal gearwheel of the gear being supported in the (support) casing.
The planet carrier is preferably arranged in the drive shaft of the rear rotor.
Further embodiments of the invention are described in the sub-claims.